I'm confused. This is exactly what https://htmx.org/attributes/hx-target/ is for since they're already using htmx. This doesn't make sense to add to the html spec unless ajax requests themselves are added such that browsers will do this automatically. Which I don't think anyone wants.
I think the point is that they don't want to have to use a full JS framework (which is what HTMX is) for this behavior.
And this is where HTMX fits in. It's an elegant and powerful solution to the front-end/back-end split, allowing more of the control logic to operate on the back-end while dynamically loading HTML into their respective places on the front-end.
But for a tech-luddite like me, this was still a bit too much. All I really want to do is swap page fragments using something like AJAX while sticking to semantically correct HTML.
EDIT: Put another way, if you look at HTMX's "motivation"s:
motivation
Why should only <a> & <form> be able to make HTTP requests?
Why should only click & submit events trigger them?
I see, I guess I get the point they're making. We can do iframe reloads based on clicks without javascript, why not div reloads. I think framing it as a way of doing this without javascript rather than without a framework would be clearer and a better argument